The present invention relates generally to a zoom optical system and an imaging system that incorporates it, and more particularly to a compact zoom optical system and electronic equipment including such a compact zoom optical system (which is designed to be built in or on, for instance, digital cameras, video cameras, digital video units, personal computers, mobile computers, cellular phones, and personal digital assistants).
In recent years, personal digital assistants called PDAs and cellular phones have enjoyed a burst of popularity, and there has been a growth in the use of systems with built-in compact digital cameras or digital video units using as imaging devices CCD (charge coupled device) sensors or CMOS (complementary metal oxide semiconductor) sensors as well. More recently, imaging devices having a lot more pixels (mega-pixel), albeit being of relatively compact size, have been developed and, with them, compact yet high-performance optical systems have been in great need.
One typical prior art optical system of small size is set forth in Patent Publication 1 or Patent Publication 2. This is a zoom optical system comprising three units of negative, positive and positive powers, each composed of one lens. Patent Publication 3 shows a small-format zoom optical system with negative power at the front unit. Patent Publication 4 or Patent Publication 5 teaches a zoom optical system comprising three units of negative, positive and negative powers, each composed of one lens.
Further, Patent Publication 6 sets forth one typical small-format zoom optical system for electronic equipment. This is a zoom optical system comprising three units of negative, positive and negative or negative, positive and positive powers, each composed of one lens, wherein the second lens unit and the third lens unit are moved for zooming. Furthermore, many other zoom optical systems using an optical element with variable refracting power have been proposed in the art. For instance, Patent Publication 7 has put forward a zoom optical system with negative power at the front unit, which employs an optical element with variable refracting power.
Patent Publication 1
JP-A-2002-55278
Patent Publication 2
JP-A-2003-177314
Patent Publication 3
JP-A-2004-226691
Patent Publication 4
JP-A-3-260611
Patent Publication 5
JP-A-2004-133058
Patent Publication 6
JP-A-2004-226691
Patent Publication 7
JP-A-64-24214
Patent Publication 8
JP-A-2001-272646